1. Field of the Invention
The invention generally relates to scratch-resistant coatings with improved cleanability, to substrates having scratch-resistant coatings that are easily cleaned, and to methods for producing such coatings. More particularly the invention relates to scratch-resistant coatings known as “easy-to-clean” coatings and to coated substrates having a hard material layer based on aluminum nitride, and to the manufacturing thereof, in particular by sputtering.
2. Description of Related Art
Various coatings for increasing scratch resistance are known from the prior art. For example, patent application DE 10 2011 081 234 A1 discloses a hard material coating on glass ceramic substrates, which has two different material phases. However, a disadvantage thereof is that the coefficient of thermal expansion of the coating and of the substrate must not differ by more than 20%. Moreover, since glass ceramics have a very low coefficient of thermal expansion, this considerably limits the number of suitable coatings. For example, the coefficient of thermal expansion of hard material layers based on nitrides or oxides, such as boron nitride is too high, so that these materials cannot be used for coating glass ceramic substrates.
A coating for enhancing scratch resistance should not only exhibit high hardness. Rather, other decisive factors for the quality of a scratch-resistant coating or of a substrate coated therewith include elasticity (modulus of elasticity), surface roughness, stress in the layer due to different coefficients of thermal expansion of the substrate and the coating, and surface properties of the substrate. Moreover it is desirable that in addition to high scratch resistance, surfaces coated accordingly such as glass or glass ceramic surfaces exhibit high resistance to wearing and polishing stress which occurs during manufacturing and also during subsequent use.
Besides increased scratch resistance, improved cleanability of the coating is relevant as well. This is particularly true for application areas such as cooktops, for which in part heavy contamination can be expected in daily use. Such contaminations must be removed from the surface without damaging the coating. Moreover, easy removal of contaminations is desired by the consumer as well. Appropriately equipped surfaces are referred to as easy-to-clean surfaces. Such surfaces have a larger contact angle compared to the non-coated substrate.